1. Field of the Invention
This invention relates to automatic door operators, and more particularly to door openers having obstruction detection devices.
2. Description of the Prior Art
There have been various types of obstruction detection devices for use in garage door operators. Most garage door operators have for many years typically included a torque sensing device as a part of the door operator. The sensing device detected whether excess torque was being used to close the garage door. Since such excess torque would probably be caused by the door attempting to close upon an obstruction that was in the path of the door, the door operator stopped and reversed the door when this excess torque was detected.
While such torque detectors were generally effective, they only worked after the door had actually encountered the obstruction, and they did not provide a means for detecting obstructions before the door has exerted excessive force on the obstruction.
Recently, increased attention has been paid to residential garage door operator safety. Legislation has been passed in several states, including Minnesota and California, and there is pending federal legislation. The purpose of this legislation is to provide additional safety features to residential garage door operators beyond the traditional torque sensing devices, so that the door does not strike obstructions that are in the path of the door. The California law requires the inclusion of a tactile garage door edge sensor, an optical sensor or similar device that, when activated, is designed to cause a closing door to open and prevent an open door from closing.
This legislation thus mandates the inclusion of an obstruction detection device for residential garage door openers that will detect the presence of an obstruction before the door applies excessive force to the obstruction and that will be connected to the door operator so that the operator takes appropriate control of the door closing when an obstruction is detected. The two most widely used obstruction detection devices of this type are edge sensors and optical or light beam sensors.
Edge sensors have been commonly used in one form for many years on elevator doors, and edge sensors have also been specifically designed for use on the bottom edge of garage doors. An electrical edge sensor device typically comprises a strip placed along the leading edge of the garage door providing a multiplicity of parallel open switches spaced along the door edge. When a small amount of pressure is applied to any spot in the door, one or more of the switches closes, producing a closed circuit. Edge sensors thus provide an open-circuit or high-level signal when no obstruction is sensed and provide a closed-circuit or low-level signal when an obstruction contacts the sensor.
Optical beam sensors work by providing a light beam across the doorway and sensing if this beam is broken by the presence of an obstruction. An optical beam sensing device typically include a infrared light emitter positioned on one side of the garage doorway and an infrared light sensor on the other side. The emitter produces a light beam that is aligned so that it extends across the doorway and strikes the light sensor on the other side. As long as the sensor detects the light beam, the sensor produces a low-level output signal to the door operator. When the light beam is broken and the sensor does not detect the presence of the beam, the sensor produces a high-level output signal indicating the presence of an obstruction in the doorway.
These obstruction detection devices are typically electrically connected to the door operator by three wires or lines: a supply line, a ground line and a signal line. The supply line typically provides a voltage supply of 20 to 30 volts from the power supply of the door operator to the remote obstruction detection device. The ground line supplies a reference ground signal from the door operator to the obstruction detection device. The signal line carries the output signal from the obstruction detection device to the door operator indicating the presence or absence of an obstruction. The voltage on the signal line is close to the supply voltage when the obstruction senses an obstruction and is close to ground when no obstruction is sensed.
As long as the door operator receives a low-level output signal from the obstruction detection device on the signal line, the operator operates the door in a normal sequence, opening and closing the door. When the door operator receives a high-level output signal from the obstruction detection device on the signal line, this is an indication that an obstruction has been detected, and the door operator alters the normal sequence of operation by stopping and reversing the door if it is closing. (If the door is already opening when an obstruction is detected, the operator continues opening the door without interruption. ) As long as an obstruction continues to be sensed by the obstruction detection device, a high-level output signal continues to be present on the signal line, and the operator will not permit the door to close.
These external obstruction detection devices are generally very effective in sensing an obstruction so that the door operator takes the appropriate action in response. However, the obstruction detection devices are only effective as long as they operate and as long as the wiring between the door operator and the detection device is in proper operating condition. If one of the wires between the obstruction detection device and the door operator breaks or is damaged or if the wires short out, the perceived signal from the obstruction detection device will be unreliable. If certain wires short or open, the signal line will contain a high-level signal which will cause the door operator to keep the door open. However, if certain other conditions occur, it is possible for the door operator to continue to sense a low-level signal on the signal line even though there is an obstruction in the doorway.
For example, if the supply line and the signal line short together, a high-level signal will be present on the signal line regardless of the presence of an obstruction. If the signal line and the ground line short together, a low-level signal will be present on the signal line regardless of the presence of an obstruction. If the supply line or the signal line is damaged creating an open circuit on either line, a low-level signal will be present on the signal line regardless of the presence of an obstruction. Similarly, if the ground line is damaged creating an open circuit on that line, a high-level signal will be present on the ground line regardless of the presence of an obstruction.